1. Field of the Invention
The invention relates to a manufacturing method of an endless metal belt and manufacturing apparatus of the endless metal belt.
2. Description of the Related Art
A method for manufacturing an endless metal belt used for a non-stage transmission or the like includes, as shown in FIG. 1, for example, a welding step for rounding and welding a workpiece steel, a cutting step for forming metal rings each having a predetermined width, a grinding step for trimming the end face of each metal ring, a rolling step for forming a metal ring having a fixed thickness and a fixed circumference, a solution heat treatment step, a circumference correction step, an ageing step, a nitriding step, and build-up step for forming an endless metal belt consisting of a plurality of layers having different circumferences.
In the circumference correction step, in particular, the metal rings are expanded and, as shown in FIG. 2, metal rings corresponding to respective layers, equal in thickness and different in circumference are formed. For example, Patent Document 1 (Japanese Patent Application Laid-Open Publication No. 11-290971) discloses a method and an apparatus for expanding a metal ring using rollers and correcting the circumference of the metal ring to a predetermined circumference.
However, due to the large expansion quantity of the metal ring in the circumference correction step, the metal ring is greatly contracted thereafter based on elastic deformation. Since the contraction quantity is proportional to the expansion quantity, the contraction quantity varies according to the circumference and the fluctuation of the contraction quantity is not constant. This, therefore, makes it difficult to maintain the accuracy of the circumference of the metal ring.
Thus, it is difficult to determine a combination for building up metal rings and the deterioration of working efficiency and the increase of working man-hour occurs. This disadvantageously pushes up manufacturing cost.